Radio relay system



May 7, 1957 J. s. WILLIAMS RADIO RELAY SYSTEM Filed Nov. 2. 1953 L. ff v UWA/.5777A ATTORNEY RADIO RELAY SYSTEM James S. Williams, Moorestown, N. J., assgnor to Radio Corporation of America, a corporation of Delaware Application November 2, 1953, Serial No. 389,573

11 Claims. (Cl. Z50-1S) This invention relates to a radio relay system, and more particularly to a relay station including a single transmitter and a single receiver which may be connected with two directional antennas so as to provide various modes of operation.

Radio relay stations for the handling of trailic in both directions on the system normally include two complete equipments, one for each direction of relaying. Each of these equipments normally consist of a directional receiving antenna, a receiver, a transmitter, and a directional transmitting antenna. By this arrangement, trailic can be simultaneously handled in both directions.

There are many instances where the tratiic to be handled by aV relay system is not sufiiciently heavy to justify the duplication of equipment necessary to simultaneously handle traffic in both directions. It is then desirable to employ a single transmitter and a single receiver which may be connected to antennas in such a way that the traiiic may be passed in one or the other of the two directions for any desired period of time. When relay stations are in remote localities, and are normally unattended, it is necessary that automatic means be provided to determine the direction in which the relay station will operate.

lt is also often desirable for a relay station to simultaneously transmit a locally originated message in both directions from the relay station. The locally originated signal may in fact be one received at an unattended relay station from, for example, a mobile transmitter. Separate receiving equipment including a Separate nondirectional receiving antenna may be provided at the relay station for this purpose. A general object of this invention is therefore to provide an improved relay station system including the minimum in equipment and yet providing for several distinct selectable modes of operation.

Another object is to provide an improved relay station normally alert to signals receivel from both of two directions, and operative automatically upon receipt of a signal from one direction to transmit the signal in the opposite direction.

A further object is to provide an improved relay sta,u tion wherein a locally originated message may be simultaneously transmitted in both directions.

A still further object is to provide an improvedrelay station including improved means for switching two antennas under various desired transmitting and receiving conditions.

In one aspect, the invention comprises a relay station having a single transmitter, a single receiver, a first directional antenna pointed in a first direction, and a second directional antenna pointed in a second direction. Either one or both of the antennas may be connected thru an impedance matching arrangement ofV relays to the receiver and the transmitter. Normally, both antennas are connected to the receiver. If a carrier wave is applied to the receiver from the rst antenna, a carrier operated relay in the receiver energizes relays which connect the transmitter to the second antenna. A message on the carrier is then relayed thru the relay station to the distant point from the second antenna. If a tone modulated carrier is applied to the receiver from the second antenna,

States Patent O Patented May '7,A 1957 a tone detector in the output of the receiver operates relays which connect the transmitter to the first antenna. Message modulation on the carrier is thus relayed by the relay station to the distant point from the first antenna. The tone modulation used to determine this direction of operation of the relay station may be a super audible frequency tone, or it may be a tone which is higher than the message modulation on the carrier, so that it is removed by means of a low pass filter. When it is desired to transmit a locally originated message, a switch is thrown which energizes relays in such a manner that the transmitter is connected to both of the antennas so that the message is simultaneously transmitted in both directions. The arrangement is such that under all of the different conditions of operation, a perfect impedance match is maintained between the various components in the system.

These and other objects and aspects of the invention will be apparent to those skilled in the art from the following more detailed description, taken in conjunction with the appended drawing, showing a presently preferred form of the system of this invention.

Referring to the drawing, a first antenna 5 is normally connected thru relay contacts 6 and 7, and thru an impedance transformer 8y to a radio receiver 9. A second antenna 10 is normally connected thru switch contacts 11 and 12, and thru impedance transformer 8 to the receiver 9. The output of a transmitter 15 may be connected thru an impedance transformer 16, relay contacts 21 and relay contacts 1S to the first antenna 5. The output of transmitter 15 may also be connected thru impedance transformer 16, relay contacts 19, and relay contacts 20 to the second antenna 10. Relay contacts 17 may connect the output of transmitter 15 to a termination 22. Relay conacts 23 may connect the output of transmitter 15 to a terminating impedance 24. Relay contacts 25 may connect the input of receiver 9 to a termination impedance 26, and relay contacts 27 may connect the input of receiver 9 to a terminating impedance 2S.

Itv will be noted that the connections described above are such that the output of the transmitter 15 is divided into two branches by impedance transformer 16, one branch being connected to termination impedance 22 or antenna 5, and the other branch being connected to terminating impedance 24 or antenna 10. It will also be noted vthat the receiver 9 has two input branches combined by limpedance transformer 8 into al single input to the receiver. One of the branches is connected to terminating impedance 26 or antenna 5, and the other branch is connected to terminating impedance 28, or the antenna 19.

The paths over which the antennas5 and 10 are connected to the receiver 9 and the transmitter 15 are made up of coaxial lines lines having a characteristic impedance of, for example, 50 ohms. The various relay contacts thus far describedy constitute conventional coaxial line switches energized by relay coils. The three sets of relay contacts associated with the first antenna 5 and included within the dotted line box 30 are, operated by the relay coils included in the dotted line box 31. Similarly, the three sets of relay contacts associated with the second antenna 10 and included within the` dotted line box 32 are operated by the three relayy coils included in the dotted line box 33. Impedance matching transformers 8 and 16 are conventional coaxial line transformers havingA three terminals each of which may be connected to, for example, a 50 ohm coaxial line to provide an impedance match in all directions. Energy applied to one of the three terminalsr is equally divided in going out t-hru the other two terminals.

The output from receiver 9 is conveyed over lead 35 `thru lowfpasslter 36'and thru switch contacts 37 tothe input of transmitter 15. Alternatively, an output from a local audio frequency message source 38 may be connected thru relay contacts 39 to the transmitter 15. A portion of the intermediate frequency'signal within the receiver 9 is conveyed from a limiter stage in the receiver to an amplifier 40 including a normally non-conducting vacuum tube having a relay coil 41 in its plate circuit. Relay contacts 42 are closed when `a radio frequency carrier is received by antenna S and applied to the receiver 9. One of the contacts 42 is connected to the positive terminal 43 of a source of unidirectional potential (not shown). The negative terminal of the source is connected to ground. The amplifier 40, :and the relay 41, 42 constitute a carrier operated relay circuit of a conventional design often incorporated Within a communications receiver of the type designated 9 in the drawing.

A part of the audio frequency output from receiver 9 on output lead 35 is also applied to a tone detector 4S including a band-pass filter and a vacuum tube. A relay coil 46 is in the plate circuit of the vacuum tube. The filter in the tone detector 45 is designed to pass a predetermined tone frequency which is used to modulate the distant radio transmitter whichrdirects a signal to the antenna 10. The amplifier tube in the tone detector 45 is normally non-conducting, but when the predetermined tone is applied thru the lter to the tube, it is rendered conductive and the current flow in the plate circuit including relay coil 46 causes relay contacts 47 to close. Relay contacts 4S are normally closed.

When it is desired to transmit the locally originated message signal from the audio source 38, a switch 50 is closed connecting the positive terminal 51 of a source of uni-directional potential thru a relay coil 52. This closes normally opened relay contacts 53 and 54, thereby connecting the positive terminal 55 of ya source of unidirectional potential to the control leads 56 and 57. Leads 56 and 57 are connected thru the relay coils in dotted line box 31 and dotted line box 33, respectively, -to ground. The energization of relay coil 52 also closes contacts 39 connecting source 38 to the transmitter 15.

The operation of the system will now be described. All of the relay contacts are shown in the drawing in the position they have when the relay station is idle but alert to a signal received on antenna 5 or antenna 10 or originated at audio source 38. When a radio frequency carrier wave, modulated or unmodulated, is received by antenna 5, the radio frequency energy is applied thru switch contacts 6, switch contacts 7 and impedance transformer 8 to the radio receiver 9. The radio frequency energy applied to the receiver 9 is heterodyned to an intermediate frequency and an output from a limiter in the receiver following the intermediate frequency circuits is applied to an amplifier 40, having relay coil 41 in its plate circuit. Amplifier 40 is biased to be normally non-conductive but is made conductive by the received signal so that relay coil 41 is energized and relay contacts 42 are closed. When relay contacts 42 are closed, a relay operating potential is applied from positive terminal 43 thru relay contacts 42, thru relay contacts 48 and thru the three relay coils within the dotted line box 33 to ground. Each one of the relay coils in dotted line box 33 is associated with one of the three sets of relay contacts in dotted line box 32. When the relay coils are energized, the movable contacts shift to the positions wherein contacts 19, 20, and 27 are closed. Of course, if the contact switch arms in dotted line box 32 are ganged, a single relay coil could be used in place of the three coils in dotted line box 33. However, the commercially available coaxial line relays are such that the arrangement shown in the drawing is preferred for practical reasons.

After the relay contacts in dotted line box 32 have been shifted from the positions shown in the drawings, it will be seen that antenna 10 is connected thru relay contacts 20, relaycontacts 19 .and impedance transformer 16 to the transmitter 15. The output of receiver 9 is connected thru output lead 35, low pass lter 36 and relay contacts 37 to the input of transmitter 15. It is thus Iapparent that the relay station is now in a condition to retransmit from antenna 10 the signal received by antenna 5. Y Y Y If a signal is received by antenna 10 including a radio frequency carrier which is modulated .by a tone having a frequency above the audio frequency band employed for message modulation, assuming the relay contacts to be in the idle but alert positions shown in the drawing, the received signal is applied from antenna 10 thru Irelay contacts 11, thru relay contacts 12 and thru the impedance transformer 8 to the receiver 9. The audio frequency output from the receiver 9 is applied over the lead 35 to a tone detector 45. The tone detector 4S includes a filter which passes the tone frequency to av normally nonconducting vacuum tube having relay coil 46 in its plate circuit. The tone renders the tube conductive and energizes the relay so that relay contacts 47 close. At the same time, the radio frequency carrier applied to the receiver 9 energizes amplifier 40 and relay coil 41 to close switch contacts 42. Under this condition, control current iiows from the positive terminal 43 thru relay contacts 42, thru relay contacts 47 and thru the relay coils lwithin the dotted line box 31 to ground. The three relay coils in dotted line box 31 are associated respectively with the three sets of relay contacts in dotted line box 30. The relay contacts in dotted line box 30 therefore shift to positions such that the antenna 5 is connected thru relay contacts 18, relay contacts 21 and irnpedance transformer 16 to the output of transmitter 15. The receiver 9 remains connected to the input of transmitter 15 by means of output lead 35, low-pass filter 36 and switch contacts 37. It is thus apparent that the radio frequency signal received by antenna 10 is retransmitted from antenna 5. Low pass filter 36 prevents the tone frequency on the carrier wave applied to antenna 10 and present inthe output 35 of receiver 9 from being passed on to the transmitter 15.

The manner in which a locally originating message may be transmitted simultaneously from both of antennas 5 and 10 will now be described, starting with the condition wherein the system is idle and alert with the relay contacts in the positions shown in the drawing, The switch 50 is closed connecting current from the positive terminal 51 thru the relay coil 52 to ground. The encrgization of relay coil A52 closes contacts 39, 53 and 54. Positive potential is then applied from positive terminal 5S thru relay contacts 54, lead 57 and the relay coils in dotted line box 33 to ground. At the same time, positive potential is Vapplied from positive terminal 55 thru contacts 53, lead 56 and the relay coils in the dotted line box 31 to ground. All of the sets of relay contacts in dotted line boxes 30 and 32 are thus shifted to the opposite positions fromthose shown in the drawing. Both antennas 5 and 10 are then connected thru the impedance matching transformer 16 to the output of transmitter 15. The output of audio source 38 is simultaneously connected thru switch contacts 39 to the input of transmitter 15. A message originating in audio source 38 is thus used to modulate the transmitter 15 and to cause a radio frequency signal to be transmitted from both of antennas 5 and 10.' v

Terminations 22, 26, 24 and 28 may be in the form of resistors connected between the inner and outer conductors of coaxial lines, the value of the resistors being equal. to the characteristic impedance of the coaxial lines. Thearrangement is such that under all of the various conditions of operation, the several circuit components are impedance matched. For example, assuming that 50 ohm coaxial lines are used between the transmitter and the antennas, and between the receiver andthe antennas, the 50 ohm output of thetransmitter 15- is matched tothe S0 ohm input impedance of the coaxial line transformer 16. With the relay contacts in the position shown in the drawing, one 50 ohm output of transformer 16 is connected thru relay contacts 17 to the 50 ohm termination 22. The other terminal of transformer 16 is connected thru relay contacts 23 to the 50 ohm termination 24. The impedance transformer 16 transforms the impedance of the two 50 ohm terminations in parallel (which result in an impedance of 25 ohms) to an impedance of 50 ohms at the terminal connected to the transmitter 15.

One terminal of the transformer 8 is connected thru relay contacts 7 and 6 to the 50 ohm antenna 5, and the other side of transformer 8 is connected thru relay contacts 12 and 11 to the 50 ohm antenna 10. It is thus apparent that under all conditions there is an impedance match between the antennas and the transmitter and receiver. Of course, there is a 50% loss in radio frequency energy when connections exist to the 50 ohm terminations 22, 26, 24 and 28. For example, a radio frequency signal received by antenna 5 is applied to impedance transformer S from which half of the energy goes to receiver 9 and the other half goes to antenna 10. Similarly, when transmitter is connected to one of the antennas 5 and 10, half of the energy goes to the one antenna, and the other half goes to one of the terminating impedances 22, 24. When the transmitter 15 is connected to both of the antennas 5 and 10, the energy from the transmitter is equally divided between the two antennas.

It has been found in the practical use of the system of this invention that the importance of maintaining a proper impedance match under all conditions of operation is very great and that the resulting energy ydivision is of very little practical importance. According to this invention, a relay system is provided having a minimum number of components and yet providing for automatic operation under various traiic conditions. in the absence of signals received by antennas 5 and 10, and in the absence of a locally orginated signal from source 38, all relay contacts return to their idle and alert positions which are shown in the drawing.

What is claimed is:

1. A radio relay station comprising, first and second antennas, a transmitter having an output divided into first and second branches, a receiver having first and second branches combined into a single input, means coupling the output of said receiver to the input of said transmitter, terminating impedances, first relay means connecting one of said irst transmitter and receiver branches to said tirst antenna and the other to a terminating impedance, second relay means connecting one of said second transmitter and receiver branches to said second antenna and the other to a terminating impedance, and means responsive to a signal received by said tirst antenna to actuate said second relay means to reverse the connections of said second transmitter and receiver branches.

2. A radio relay station as defined in claim 1 wherein said last named means comprises a carrier operated relay circuit.

3. A radio relay station as defined in claim 1 wherein said last named means comprises a tone detector relay circuit.

4. A radio relay station as dened in claim 1, and in addition, means to simultaneously actuate both of said irst and second relay means.

5. A radio relay station as defined in claim 4, and in addition, a local source of signals, and means to apply the output of said source to the input of said transmitter.

6. A radio relay station as defined in claim 1 wherein said transmitter and receiver branches each comprise two terminals of a three terminal impedance matching branching transformer.

7. A radio relay station comprising, rst and second antennas, a transmitter having an output divided into rst and second branches, a receiver having first and second branches combined into a single-input, means coupling the output of said receiver to the input of said transmitter, relay means including contacts connecting said two antennas respectively to two of said four branches, and impedance means connected by said relay contacts to the other two of said four branches.

8. A radio relay station comprising, rst and second antennas, a transmitter having an output divided into rst and second branches, a receiver having irst and second branches combined into a" single input, means coupling the output of said receiver to the input of said transmitter, terminating impedances, rst relay means connecting one of said rst transmitter and receiver branches to said rst antenna and the other to a terminating impedance, second relay means connecting one of said second transmitter and receiver branches to said second antenna and the other to a terminating impedance, a carrier operated relay circuit coupled to said receiver and operative to actuate said rst relay means, and a tone detector relay circuit also coupled to said receiver and operative to actuate said second relay means.

9. A radio relay station comprising, first and second antennas, a transmitter having an output divided into first and second branches, a receiver having rst and second branches combined into a single input, means coupling the output of said receiver to the input of said transmitter, iirst switch means connecting one of said tirst transmitter and receiver branches to said iirst antenna, second switch means connecting one of said second transmitter and receiver branches to said second antenna, and means responsive to a signal received by said first antenna to actuate said second switch means to reverse the connections of said second transmitter and receiver branches.

l0. A radio relay station comprising first and second antennas, a transmitter having an output divided into tirst and second branches, a receiver having lirst and second branches combined into a single input, means coupling the output of said receiver to the input of said transmitter, terminating impedances, first relay means connecting said first receiver branch to said iirst antenna and said iirst transmitter branch to a terminating impedance, second relay means connecting said second receiver branch to said second antenna and said second transmitter branch to a terminating impedance, and means responsive to a signal received by said irst antenna to actuate said second relay means to connect said second receiver branch to a terminating impedance and to connect said second transmitter branch to said second antenna.

1l. A radio relay station comprising irst and second antennas, a transmitter having an output divided into rst and second branches, a receiver having first and second branches combined into a single input, means coupling the output or said receiver to the input of said transmitter, iirst switch means connecting said first receiver branch to said lirst antenna, second switch means connecting said second receiver branch to said second antenna, means responsive to a signal received by said first antenna to actuate said second switch means to connect said second transmitter branch to said second antenna and to disconnect said second receiver branch from said second antenna, and means responsive to a signal received by said second antenna to actuate said first switch means to connect said first transmitter branch to said iirst antenna.

References Cited in the tile of this patent UNITED STATES PATENTS 1,570,755 Laynes Jan. 26, 1926 2,189,549 Hershberger Feb. 6, 1940 2,472,585 Hailes June 7, 1949 2,671,166 OBrien Mar. 2, 1954 

